R Notes Basic
Aphorisms
  1. incompletely initialized arrays
  2. The best reason to build your own binaries is to get better performance out of R.
  3. sudo yum install R.i386
  4. R -g Tk
  5. R --quiet or R -q
  6. The commands that you type into the console are called expressions. A part of the R system called the interpreter will read the expressions and respond with a result or an error message.
  7. Incidentally, R has quite a bit in common with LISP: both languages allow you to compute expressions on the language itself, both languages use similar internal structures to hold data, and both languages use lots of parentheses.
  8. R CMD BATCH generate_graphs.R
  9. R CMD BATCH generate_graphs.R generate_graphs_'date "+%y%m%d"'.log
  10. On Linux and Mac OS X systems, the command line uses the GNU readline and includes a large set of editing commands.
  11. RExcel, http://rcom.univie.ac.at
  12. Rapache, http://biostat.mc.vanderbilt.edu/rapache/
  13. Rserve, http://www.rforge.net/Rserve/index.html
  14. ESS, http://ess.r-project.org/
  15. Preallocate Memory by setting the length, nrow, ncol, or dim attributes for an object. v = c(NA) length(v) = 100000 for(i in 1:100000){v[i] = i;}
  16. gc() performs garbage collection and displays memory statistics.
  17. object.size(obj) returns the approximate size of the object obj
  18. memory.profile() displays information on memory usage by object type
  19. (MS Windows only) memory.size() returns how much memory in MB R is using on Windows OS.
  20. (MS Windows only) memory.limit(size=1280) sets the memory limit to 1280MB on Windows OS.
  21. mem.limits(nsize=NA, vsize=NA) is used to get or set memory limits on Linux and Mac OS.
  22. library() # list installed libraries in a separate window
  23. installed.packages() # return a char vector composed of names of installed libraries
  24. search() # return a char array of search paths, begin with .GlobalEnv. Packages in the search path are prefixed with package:.
  25. isLoaded = paste("package", myPackageNames, sep=":") %in% search() # return a bool array of whether a package is loaded.
  26. loadedPackages = unique(installed.packages()[paste("package",installed.packages(),sep=":") %in% search()]) # return a char vector of currently loaded packages, which must be a subset of installed packages.
  27. with(myTable,subset(myTable, sex == "male", select=c("height","weight"))) # this code emulates SQL's select statement SELECT height,weight FROM myTable WHERE sex='male';
  28. merge(table1, table2, by=commonField) # this code emulates SQL's join statement SELECT * FROM table1, table2 WHERE table1.commonField = table2.commonField;
  29. myTable[c(T,F),] # retrieves the odd rows of myTable. Boolean values in index are recycled to match the dimension.
  30. stop("someErrorMessage"); # Error: someErrorMessage and programming halts at the line
  31. options(warn=1);warning("someWarningMessage"); # warn=1 => print waring message immediately; warn=0 => print warning message when returned to top level control; warn < 0 => ignore warning; warn > 1 => same as stop("someErrorMessage")
  32. options()$warn # to view the specific option item
  33. .Machine # a list of machine constants. e.g. .Machine$double.eps